1. Because of the drive letter allocation in I have never used bootsect, so I can’t answer

3. Boot from drive x, which is the system drive, so the drive letter is drive c. If you install XP directly under the PE of the mobile hard disk, then the boot ntldr of xp will be installed under the mobile hard disk instead of the x disk. When you start xp from the x disk, it will fail. Note that drive letter assignment has nothing to do with the partition table.

4. "If you install XP directly under the PE of the mobile hard disk, your system disk will always be the X disk. So we have to start PE from the local disk." This is wrong and should be said. "If you install XP directly under the PE of the mobile hard disk, then your system disk will always be the mobile hard disk. So we need to start the PE from the local disk." Moreover, mbr does not belong to any partition, and mbr is located on track 0 of the hard disk. Cylinder 0 sector. After mbr comes the hard disk partition. pbr is located in the first sector of each partition.

5. I haven't used vista or win7, so I can't be sure. Because the XP installation process may detect pbr, if it is found that pbr is a higher version, can the installation process continue? Not sure.

6. The mbr is written when the partition is made. The installation of the Windows system will not cause the mbr to change unless the partition is repartitioned. Personal understanding. If you have xp and vista installed on different hard drives, you can compare their mbrs to find out.

7. The higher version can definitely cover the lower version, I agree with you. mbr I personally think it will not be changed.